Method and apparatus for contemporaneously fractionating a plurality of hydrocarbon mixtures



Nov. 19, 1968 R. G. GRAVEN 3,412,016

METHOD AND APPARATUS FOR CONTEMPORANEOUSLY FRACTIONATING A PLURALITY OF HYDROCARBON MIXTURES Filed March 29, 1967 mm H V w m M w. m4 T 0 W m W N& um 7 m m m W m w u ma nt i mmm Mm m .15 e E 0 wmw mm .C /6 LPFE m OW m wmm Hs v. 8N T B F 4 Q m 5 w 5 B 5 M 5 |||||||l|||| D o E 7 w c w n mm p m T United States Patent METHOD AND APPARATUS FOR CONTEMPORA- NEOUSLY FRA'CTIONATING A PLURALITY OF HYDROCARBON MIXTURES Richard G. Graven, Armonk, N.Y., assignor to Mobil Oil Corporation, a corporation of New York Filed Mar. 29, 1967, Ser. No. 626,754 Claims. (Cl. 208354) ABSTRACT OF THE DISCLOSURE A single fractionating tower design is provided for obtaining at least two separate bottoms products thereof each having a desired composition by providing in the lower portion of the tower two or more compartments for retaining the separate liquid bottoms fractions. The tower is provided with a common refluxing section in the upper portions in combination with an intermediate tray arrangement about the upper end of the vertical bafile or baffles to provide for controlled distribution of liquid refluxed to the upper part of each compartment.

Background of the invention Heretofore, it has been a general practice in the production of reformates to employ blocked-out operation or two or more reforming systems in parallel flow arrangement. That is to say, the reforming unit when operated under blocked-flow reforming conditions was necessarily an intermittent operation operated generally at different conditions as required to produce a reformate product having a desired predetermined octane rating, That is, after operation under one set of reforming conditions for a period of time required to meet the demand for reformate so produced, the reforming conditions were then changed to produce a stabilized reformate product having another desired octane rating. While blocked-flow operation required substantially only one recovery system, i.e., one liquid-gas separator and one stabilizer and was regarded as relatively economic in this respect, nevertheless the reforming unit was inefficient since it employed equipment sized to accommodate the most severe or maximum capacity operating condition for a given severity of operation. As a result, each piece of equipment (with minor exceptions) would be utilized at optimum design capacity conditions only a part of the on-stream time. This necessarily also increased the cost of the unit over a unit in which all pieces of equipment could be utilized at or near full capacity at all times.

In a similar manner, the products of parallel arranged reforming units producing contemporaneously a lowoctane reformate and a high-octane reformate have been recovered and stabilized in separate equipment this requiring duplication of the recovery equipment as well as other processing equipment. This duplication was necessarily expensive.

Summary of the invention The present invention relates to the method and apparatus for effecting simultaneous stabilization of at least two different hydrocarbon feeds, substantially liquid at desired fractionating temperatures. The hydrocarbon materials of the same or different composition to be handled or stabilized by the present invention are introduced separately to the upper portion on different sides of a vertical baffle separating the lower portion of the stabilizer tower of the present design into at least two separate bottom compartments. The tower of the present invention, therefore, is provided with compartmented stripping sections in the lower portion thereof having a common rectification or reflux section thereabove.

The present invention also provides among other things for heating at least two liquid materials separately in the lower portion of the tower to a temperature at which lowboiling components of each are volatilized. The volatilized componnets then pass overhead and upwardly through the separate compartments into a common rectification section thereabove. In the common rectification zone, higher boiling components of the separate charges are separated from low-boiling components under refluxing conditions so that materials boiling above a certain cut point such as (1 hydrocarbons are returned to the compartments forming the lower portion of the tower. It is to be understood that the tower may be designed and operated under conditions to maintain substantially any desired cut point in the hydrocarbon constituents passed thereto so that C C or C or heavier hydrocarbons will be retained with the liquid product fractions recovered from the bottom of the separate compartments.

Brief description of the drawing The drawing is a graphic representation in elevation of a fractionating or stabilizer tower of the present invention having at least two separate bottom compartments formed by a common vertical baflle therebetween lying below about trays 14 and 14a identified therein. The drawing also graphically represents the segregated or compartmented fractionation section between trays 19-20 and trays 14- 14a, it being understood that a plurality of trays not shown are maintained within this space. The common enriching, reflux or rectification section forming the upper portion of the tower is represented in the drawing between trap-01f pan 13 and the uppermost tray 12. Auxiliaries such as cooling means for condensing the condensible components of the overhead and separating the condensate from gas in an accumulator or knock out drum and the reboiler means for maintaining a desired temperature in each bottoms compartment are also graphically shown, However, means for providing suitable indirect heat exchange between withdrawn compartment product and liquid feed material passed to the tower is not shown even though contemplated. It is believed that such heat exchange means and arrangements are well known to those skilled in the art.

Description of a specific embodiment Referring to the drawing by Way of example, a fractionating or stabilizer tower 11 is represented. The tower of the present invention comprises an upper common enriching section above tray 14 and two separate fractionation sections C and D formed by baflle 48 between tray 14 and trays 1920 in the bottom of the tower. Two separate bottoms compartments A and B are shown for collecting liquid product. It will be observed that the vertical bafile or wall 48, extending from the bottom of the tower to an upper intermediate point thereof and above tray 14 divides the tower in the particular showing into stripping or rectifying compartments C and D above bottoms compartments A and B. Of course, more than one vertical baifie arrangement can be employed to provide more than the two compartments shown on the drawing and usually four compartments or less. Thus, more than two feeds can be directed to separate compartments in said stripping section. It is preferred to employ a bathing arrangement to provide two compartments in the stripping chamber.

In the arrangement shown, one hydrocarbon fraction (feed one) such as an unstabilized reformate efll-uent fraction flows through pipe 50 under control of valve 51 and actuated by flow control 52 to one or a plurality of distributor inlet pipes controlled by valves 59, 53 and for introducing the feed onto feed trays as desired about the upper end of baflle 48. A second hydrocarbon fraction (feed one) which may also be an unstabilized reformate efliuent fraction flows through pipe 54 under control of a valve not shown to one or a plurality of distributor pipes controlled by valves 64, 55 and 65 for discharge -on or about trays 18 and 14a arranged about the upper end of baflle 48. The less-volatile high boiling portions of feed one overflows a suitable weir attached to each fractionating tray and flows generally downwardly through the compartment between the wall of the vessel 11 and baflle 48 in compartment C. In the passage of the liquid from feed tray 14, or alternately 17 downward, the high boiling liquid portion of feed one contacts vapors rising upwardly through the compartment until it reaches its bottoms reboiler section A. A temperature control device or other suitable sensor 66 having its sensor in compartment C actuates feed controller 67 which in turn regulates valve 33 and the flow of a heating medium passing in line 31 to indirect heat exchanger 29. In exchanger 29 the temperature of the bottoms product flowing through pipe 23 and pipe 27 is adjusted in an amount to provide required reboiler heat or heat of vaporization to the liquid in compartment A of tower 11. The liquid feed introduced to the upper part of compartment C flows downwardly over a plurality of trays to tray 19. Upon reaching tray 19 the liquid flows downwardly between wall 48 and the vertical wall of tray 19 into a seal pot 21. The collected liquid portion of the feed overflows seal pot 21 into the bottom reboiler compartment A. In bottoms compartment A the liquid level is maintained substantially constant by means of level control 70 and actuating valve 25 controlling the flow of bottoms product withdrawn through pipe 23 for further processing or distribution as desired.

In a similar manner the liquid portion of feed two introduced by pipe 54 flows over the weir of tray 14a or 18 and downwardly through compartment D containing a plurality of trays to tray 20 and thence to seal pot 22. From seal put 22 the less volatile portion of feed two flows into reboiler compartment B. A level controller 71 maintains a substantially constant level of liquid in hottoms compartment B by regulating valve 26 in pipe 24. Liquid in pipe 24 is withdrawn for further processing or distribution as desired. The liquid hydrocarbon product in both bottom compartments A and B are maintained at a. desired elevated temperature for the pressure existing therein so that desired low boiling components of the stabilized hydrocarbons therein will be taken overhead.

The stabilizer tower arrangement above briefly described is suitable for producing a low-octane bottoms product and a high-octane bottoms product simultaneously. In a particular example, low-octane unstabilized reformate is introduced on feed tray 17 and a high-octane unstabi'ized reformate is introduced on feed tray 13. Liquid hydrocarbons thus introduced overflow weirs 75 and 76 of the respective trays 17 and 18 and downwardly through the passageways 77 and 78 respectively formed with baflle 48. Temperatures at this point in the tower are adjusted or maintained so as to separate out desired hydrocarbon components of at least C and heavier hydrocarbons so that an overhead comprising C and lighter hydrocarbons can be removed. The liquid reformate of feed one flows downwardly through compartment C to tray 19 and thence through the passage 79 and into liquid seal pot 21. The liquid reformate of feed two also flows downwardly through compartment D to tray 20 and thence through passage 80 into liquid seal pot 22. From seal pots 21 and 22 respectively, the liquid reformate of feed one and the liquid reformate of feed two flow into their respective bottoms compartments A and B. In bottoms compartments A and B the liquid retormates are heated by circulating a portion of the reformate through suitable reboilers shown to maintain the liquid at a desired temperature for removal of undesired lighter hydrocarbons.

The vaporized lighter hydrocarbons together with en- 7 trained heavier hydrocarbons flow upwardly from compartments A and B through rectification sections C and D where each comes in contact with cooler liquid feed in the upper part of the tower.

The volatile hydrocarbons removed from compartments C and D above trays 14 and 14a pass overhead into a common rectification section comprising a plurality of alternately staggered and vertically disposed trays 12. In the upward flow of volatile hydrocarbons through the tower, the low-octane reformate feed one combined with condensed liquid hydrocarbons withdrawn from trap-off pan 13 by pipe 61 contact the hydrocarbon vapors as they pass upwardly through trays 14 and 14a. The use of trap off pan 13 permits effective control refluxing within the tower 11. The condensed volatile hydrocarbons in trap-off pan 13 are recycled through conduits 56 and 61 and are controlled by flow controls 62 and 57. Under the conditions maintained in the tower, the recycled hydrocarbons are revol-atilized on trays 14 and 14a to assist in separating vapor from liquid hydrocarbon in the feeds. The amount of hydrocarbon in pan 13 boiling above the desired liquid initial boiling point, as for example C is minimal. This is accomplished by maintaining the desired temperature and pressure within tower 11 and by hydrocarbon feed control. The level to which the feed is introduced into tower 11 depends upon the degree to which it is in vapor form. Thus, when a greater amount of the hydrocarbon feeds are in vapor form, the feeds are introduced to the tower 11 through the lowermost feed inlets regulated by valves 60 and 65. Should the higher boiling portion of the feeds be volatilized, upon entering the tower 11, they will be condensed prior to reaching pan 13. When prac tically all of the feeds are in liquid form, they are introduccd to tower 11 through conduits 58 and 63. In this manner, a greater degree of separations of vapor and liquid is eflected due to a greater number of trays being more fully utilized within the tower 11.

Since a difference in octane rating between the lowoctane reformate feed one and the high-octane reformate feed two lies in the composition and relative concentrations of C and heavier aromatics and paraflins, separation of the volatiles removed therefrom may be effected in a common rectification section above trays 14 and 14a. Accordingly, above trays 14 and 14a, the volatiles are mixed and stripped of C and heavier hydrocarbons by subjecting the volatiles to contact with C and alighter reflux condensate pumped from accumulator 38 by pump 42 through pipe 43 under control of valve 45 regulated by level control 73.

The overhead, comprising C but for the most part C and lighter hydrocarbons, is removed from tower 11 by pipe for passage through condenser 36 and pipe 37 to an accumulator or knock out drum 38. In accumulator 38 the uncondensed gas, e.g. hydrogen, C and C hydrocarbons are separated from. liquid condensate and withdrawn by conduit 39 under control of valve 40 which is regulated by pressure control 74. The C and heavier hydrocarbons (condensed in cooler 36) flow from accumulator 38 through pipe 41 to the suction side of pump 42. Pump 42 discharges the aforesaid 0.; and heavier hydrocarbons into pipe 43 under the control of valve 45, regulated by level control 73 and pipe 46 controlled by valve 47 responsive to level controller 72. A portion of the condensed C and heavier hydrocarbons in pipe 43 flows through pipe 44 to tower 11 to serve as reflux therein. The balance of the liquid C and heavier hydrocarbons flows through pipe 46 under control of valve 47 to storage, distribution, processing and the like.

It is to be understood that the apparatus of tower 11 above discussed comprises a cylindrical tower which may be of larger diameter in the lower portion housing the segregated compartments than in the upper portion thereof housing the common rectification section of the tower. It is also to be understood that the horizontal tray members employed in the lower portion of the tower are annular and circular 'fractionating trays which are alternately staggered in vertical arrangement to provide a tortuous path for down flowing liquid against rising vaporous material. It is also to be understood that the fractionating tray members employed throughout the towers may be any one of a number of the different types of fractionating trays known and available in the industry today such as bubble cap, sieve or perforated trays, flexitrays, float-valve trays and ripple trays.

In the design of the tower apparatus for efiecting the dual rectification herein described, it is important to the operation of the tower to provide for vaporization flexibility at the point of hydrocarbon feed inlet to the tower about the upper end of the vertical bafiie number employed therein, so that a desired initial boiling point of the rectified reformate product can be varied substantially at will.

While the present invention has been briefly discussed with specific reference to stabilizing reformates having diiferent octane ratings, those skilled in art will recog nize that the concept of producing a common overhead while producing two separate bottoms products having different compositions can be applied to many hydrocarbon feeds. Accordingly, the present invention can be employed advantageously in a great many situations in which two or more diiferent =feeds, which are at least partially liquid at fractionating temperatures, are to be stripped of low boiling components so as to produce two separate bottoms products having substantially the same or different initial boiling point. Furthermore, the liquid portion of the hydrocarbon materials may have ditferent or substantially the same boiling range, and diatferent compositions. For example, low-octane C and heavier reformate differs in the concentrations of aromatics, naphthenes, and paraflins from high-octane C and heavier reformate.

What is claimed is:

1. A fractionating tower for simultaneously fractionating a plurality of separate hydrocarbon fractions introduced thereto which comprises (a) a stripping chamber containing a plurality of alternately arranged vertically spaced apart stripping trays positioned therein,

(b) a rectification chamber positioned above said stripping chamber and containing a plurality of vertically spaced apart fractionating trays,

(c) the upper end of said stripping chamber being in open communication with the bottom of said rectification chamber and spaced apart from one another a sufficient distance to provide an annular trap-0E pan positioned therebetween,

(d) feed inlet means comprising a plurality of feed inlet conduits positioned for introducing separate hydrocarbon fractions into the upper portion of said stripping chamber but beneath said rectification chamber, said feed inlet conduits being associated with a plurality of vertically spaced apart stripping trays positioned in the upper portion of said stripping chamber,

(e) at least one substantially vertical transverse bafile means extending upwardly from the bottom of the stripping chamber to above the uppermost feed inlet conduit and terminating below the trap-off pan thereby separating said stripping chamber into at least two separate stripping sections in open communication with one another above the upper end of said bafile,

(f) a vapor outlet means positioned in the upper portion of said rectification chamber and means for recycling vapor condensate to a tray in the upper portion of said rectification chamber,

(g) conduit means for withdrawing liquid from the bottom portion of each of said separate stripping sections and means for returning heated material thereto, and

(h) conduit means for transferring liquid from said trap-ofi pan to the uppermost tray positioned about the upper end of said vertical bafile member in each of said stripping sections.

2. The fractionating tower of claim 1 wherein the plurality of feed inlet conduits for each feed material introduced to the separate stripping sections are vertically spaced apart from one another and each inlet conduit is associated with a different stripping tray positioned in the upper portion of each stripping section.

3. A process for simultaneously fractionating a plurality of separate hydrocarbon fractions into liquid and vapor components in a common fractionating tower which comprises separately introducing a plurality of heated hydrocarbon fractions into the upper portion of separate stripping sections positioned in the lower portion of a common fractionating zone so as to maintain the liquid components of each hydrocarbon fraction separate from one another and recovering from the upper portion of said fractionating zone the vaporous components of each of said hydrocarbon fractions as a combined vaporous fraction, passing the vaporous components from each of said heated hydrocarbon fractions upwardly through a common rectification zone, recovering condensed refluxed liquid in the lower portion of the rectification zone, passing condensed liquid from the lower portion of the rectification zone to the upper portion of each of said stripping zones as reflux liquid thereto, separately removing stripped liquid components from the lower portion of each of said stripping sections and returning a portion thereof in heated condition to the bottom portion of each section from which obtained to maintain desired temperatures therein and recovering vaporous materials from the upper portion of said rectification section, cooling said vapors thus recovered to form a condensate fraction and returning a portion of said condensate to the upper portion of said rectification section as reflux.

4. The process of claim 3 wherein the conditions of operation between the point of feed inlet and the lower portion of the rectification section are selected to concentrate C and higher boiling hydrocarbons in the liquid product withdrawn from the lower portion of each stripping section.

5. The process of claim 3 wherein the vapors recovered from the rectification section boil below about C hydrocarbons.

References Cited UNITED STATES PATENTS 2,l34,882 11/1938 Monro 196-132 2,651,601 9/1953 Taff et al 208-l02 3,071,520 1/1963 Smalling 196-132 3,110,663 11/1963 Miller 208364 3,314,879 4/1967 Lacy et a1 208352 DELBERT -E. GANTZ, Primary Examiner.

H. LEVINE, Assistant Examiner. 

